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Near shore oceanographic conditions off SW Portugal in summer 2006 and 2007 from satellite and in situ data

Paulo B. Oliveira(1), M.Manuel Angélico(1), Joana Fernandes(2), João Castro(2) and Teresa Cruz(2)

(1) INRB/IPIMAR - Investigação das Pescas e do Mar, Av. Brasilia, 1449-006 Lisboa, Portugal
(2) Universidade de Évora, Av. Vasco da Gama, Sines, Portugal


Data from two successive summers are used to characterize the nearshore oceanographic conditions south of cape Sines in the SW Portuguese coast. The observed time evolution of the satellite-derived sea surface temperature (SST) and chlorophyll-a (chl-a) patterns show that the near shore patterns are very sensitive to the intensity and temporal structure of the upwelling favourable winds. Stronger and more variable winds in 2007 favoured the occurrence of more events of low SST and high chl-a concentrations in the study area. The full resolution MERIS data revealed the presence of small-scale flow structures in the lee of the cape resulting from the interaction of the coastal jet and coastal morphology. The high spatial resolution of the MERIS instrument allowed to infer the representativeness of the point current measurements of the moored current meter and delineate the shadow area south of cape Sines where chl-a values were usually higher than offshore and north of the cape. The comparison between the MERIS (algal_1 and algal_2) and MODIS chl-a estimates showed that, despite the similar spatial patterns, MODIS estimates are typically higher in the near shore region. In some images, very high MODIS chl-a values (chl-a > 5 mg/m3) close to the coast lead to spatially averaged chl-a estimates in the nearshore region that are double of the MERIS estimates. The oceanographic conditions associated to this differences as well as the differences between the two MERIS algorithms are presented and discussed.


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry